Messages in this thread | | | Date | Thu, 14 May 2020 17:09:34 -0500 | From | "Gustavo A. R. Silva" <> | Subject | Re: [PATCH perf/core] perf intel-pt: Fix clang build failure in intel_pt_synth_pebs_sample |
| |
On Thu, May 14, 2020 at 12:06:48PM -0700, Ian Rogers wrote: > On Thu, May 14, 2020 at 8:01 AM Gustavo A. R. Silva > <gustavoars@kernel.org> wrote: > > > > On Thu, May 14, 2020 at 10:10:30AM -0300, Arnaldo Carvalho de Melo wrote: > > > Em Wed, May 13, 2020 at 06:47:38PM -0500, Gustavo A. R. Silva escreveu: > > > > Fix the following build failure generated with command > > > > $ make CC=clang HOSTCC=clang -C tools/ perf: > > > > > > > > util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > > > struct branch_stack br_stack; > > > > ^ > > > > 1 error generated. > > > > > > > > Fix this by reordering the members of struct br. > > > > > > Yeah, I noticed that as far back as with ubuntu 16.04's clang: > > > > > > clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final) > > > > > > util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU > > > extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > > struct branch_stack br_stack; > > > ^ > > > 1 error generated. > > > > > > > > > Will fold this with the bug introducing the problem to avoid bisection > > > problems. > > > > > > > I agree. Also, the commit hash of the "Fixes" tag only applies to the > > perf/core branch and, I guess that might create confusion. > > > So while this fixes the warning I believe it breaks the intent of the code. > > tools/perf/util/branch.h: > struct branch_stack { > u64 nr; > u64 hw_idx; > struct branch_entry entries[]; > }; > > tools/perf/util/intel-pt.c: > struct { > struct branch_stack br_stack; > struct branch_entry entries[LBRS_MAX]; > } br; > > The array in br is trying to extend branch_stack's entries array. You > might have to do something like: > > alignas(alignof(branch_stack)) char storage[sizeof(branch_stack) + > sizeof(branch_entry) * LBRS_MAX]; > struct branch_stack *br = &storage; > > malloc/free may be nicer on the eyeballs. >
Yep, I'd go for zalloc/free. There are a couple of places where dynamic memory is being allocated for struct branch_stack:
tools/perf/util/cs-etm.c-256- if (etm->synth_opts.last_branch) { tools/perf/util/cs-etm.c:257: size_t sz = sizeof(struct branch_stack); tools/perf/util/cs-etm.c-258- tools/perf/util/cs-etm.c-259- sz += etm->synth_opts.last_branch_sz * tools/perf/util/cs-etm.c-260- sizeof(struct branch_entry); tools/perf/util/cs-etm.c-261- tidq->last_branch = zalloc(sz);
tools/perf/util/thread-stack.c-148- if (br_stack_sz) { tools/perf/util/thread-stack.c:149: size_t sz = sizeof(struct branch_stack); tools/perf/util/thread-stack.c-150- tools/perf/util/thread-stack.c-151- sz += br_stack_sz * sizeof(struct branch_entry); tools/perf/util/thread-stack.c-152- ts->br_stack_rb = zalloc(sz);
there is even function intel_pt_alloc_br_stack().
Just out of curiosity, why the need of such a hack in this case (the on-stack extension of branch_stack's entries array)?
Thanks -- Gustavo
| |